What Overprint Means
Every object in a print file makes a decision about the ink underneath it. The default decision is to knock out: the object punches a hole through every separation below it, so the only ink that lands on the paper in that spot is its own. Set the object to overprint and nothing gets removed. It prints on top of whatever is already there.
For ordinary CMYK artwork, knockout is exactly what you want. It is how a yellow shape stays yellow over a blue background instead of printing green. Specialty inks are different. HP White, HP Metallic, HP Foil and HP Gloss are extra separations whose whole job is to combine with your artwork: white goes under an image so it reads on dark stock, metallic goes under color so the color shimmers, foil and gloss go over the top. A specialty ink that knocks out the CMYK cannot do any of that. It just leaves a hole.
The Rule
Every element filled with an HP specialty ink is set to Overprint Fill (and Overprint Stroke if it has a stroke). Everything else in the file stays at its default. That one habit is most of what this module is about.
Overprint vs Knockout
The two settings look identical on screen until you turn on Overprint Preview, which is why the difference catches so many people at the proof stage rather than in the file. Here is the same metallic disc on the same CMYK field, both ways.
Knockout (the default)
The disc cuts a hole in every separation beneath it. On press, only metallic ink lands inside that circle. Shift the metallic a hair off register and a sliver of bare paper shows along one edge.
Right for: ordinary CMYK objects, and anything that must print as exactly its own swatch.
Overprint
The disc prints on top of the field with nothing removed. Metallic lands over (or under) the CMYK, and a hair of drift lands on artwork rather than on paper, so it disappears.
Right for: every HP specialty ink, and the classic prepress case of small black type over a color background.
One thing worth knowing: overprint changes color when it is applied to CMYK objects. A 100% yellow shape set to overprint over a cyan background prints green, because both inks are now on the paper. That is the reason the rule above says specialty inks and not everything.
Setting Up Overprint for HP Specialty Inks
A specialty ink element needs three things to be right: the exact spot color name, the right place in the file, and the overprint attribute. Miss any one of them and the press either cannot find the separation or prints a hole where the effect should be.
Create the spot color with its exact name
Our workflow finds each specialty separation by name, so the name has to match to the
character: HP White 1, HP Metallic, HP Foil or
HP Gloss. Set the swatch type to Spot. The CMYK build you give it is only a
stand-in for your screen. We use 5/5/5/5 for white so it is visible against the page,
and something like 50% black for metallic.
Put the element on its own layer, above the CMYK
Keep specialty inks on a named layer of their own. When the specialty ink should follow existing artwork, the usual route is to copy the CMYK element and Paste in Place on the specialty layer, then fill the copy with the spot color. White ink goes on top in the file even though it prints underneath: our software reverses the order on press.
Turn on Overprint Fill (and Overprint Stroke)
Select the specialty elements and open the Attributes panel. In Illustrator that is Window > Attributes; in InDesign it is Window > Output > Attributes. Check Overprint Fill. If the object has a stroke, check Overprint Stroke as well, or the stroke will knock out while the fill does not.
Keep the HP inks as the only spot colors
Convert every other PMS or spot color in the file to CMYK, and convert fonts to outlines. The HP inks are the only separations that should survive as spot colors in the exported PDF.
| Spot name | Where it sits in the file | How it prints |
|---|---|---|
| HP White 1 | Above the artwork it backs, contracted about 2 px under images and text | First, under the CMYK, so color reads on dark or clear stock |
| HP Metallic | A copy of the CMYK element, pasted in place above it | Under the CMYK for metallic color; on its own for silver |
| HP Foil | Above the CMYK, with a printed proof planned | Over the CMYK, or under it when color is printed onto a printable foil |
| HP Gloss | Above everything, usually over an HP White 1 base | Last, as a spot gloss over the finished artwork |
All four rows share one setting: Overprint Fill on, Overprint Stroke on wherever there is a stroke.
Photoshop is the exception. There is no overprint checkbox, because a spot channel is its own plate by construction and always prints over the composite. If your job is built entirely in Photoshop, follow our spot channel guide in the sidebar and keep the foil or white file separate from the CMYK file. If it is a layout job, do the specialty ink work in Illustrator or InDesign where the attribute exists.
Worked examples, with screenshots at every step:
- Metallic Ink on Coated Stock walks the metallic-under-CMYK setup end to end, including the Attributes panel.
- Red Foil with White Ink has two specialty spot colors in one file, and both must overprint.
- Foil Only is the simplest case: one HP Foil separation, one checkbox.
Above or Below: Why Overprint Keeps the Order Open
On press, the order the separations go down is a real choice, and it changes the piece. Metallic under the CMYK gives you metallic color: a muted shimmer that shows through the ink wherever the artwork is light. Metallic over the CMYK gives you silver highlights sitting visibly on top of the printed image. Same artwork, two different results.
Overprint is what makes that our choice at the press rather than a decision frozen into your file. With no knockout hole, nothing in the CMYK depends on which pass comes first, so the same PDF can print either way. Toggle the demo to see both.
The file still has to tell us which look you are after, so say so in the job notes. Lighter colors make better metallic color than dark ones, which stop reading as metallic at all, and we will want to run a printed proof on metallic color work before the full run.
Registration and Specialty Ink Layers
Each separation is laid down as its own pass, and the sheet moves a hair between passes. That is registration, and every printer on earth has some. What overprint decides is where that hair of movement ends up. With a knockout, the hole and the ink that was meant to fill it no longer line up, and you get a white sliver of paper along one edge. With overprint, the drift lands on artwork instead of paper and vanishes into it. The Mars sample has a side-by-side registration demo that shows exactly this.
A few habits that keep specialty layers looking clean:
- Choke the white. When white sits under an image or text, contract the white shape by about 2 px so that drift never pushes white out past the edge of the color.
- Give the ink somewhere to hide. Hairlines and very small type in a specialty ink have no artwork around them for a shift to disappear into. Keep specialty elements at a weight that survives a little movement.
- Foil next to color: leave a gap. When foil and CMYK are not meant to overlap, keep them apart. We do not hold tight registration between the two, so a design that depends on them meeting exactly will not meet exactly.
- Color on foil: overprint it, and proof it. Printing CMYK onto a silver foil is a beautiful effect and a registration-sensitive one. Set the color to overprint the foil and plan on a printed proof.
Previewing Overprint in Adobe Applications
By default your screen lies about overprint. Illustrator and InDesign draw every object as if it knocked out, whatever its attribute says, and the HP inks display as whichever CMYK stand-in you gave the swatch. Two views fix that, and we recommend both before you export.
View > Overprint Preview
Available in both Illustrator and InDesign. Overprinting objects now composite over what is beneath them, so a white stand-in over an image will darken or tint. That is the preview honoring the overprint, not a picture of how white prints. What you are checking is that the artwork under the specialty element is still there.
Separations Preview
Illustrator: Window > Separations Preview. InDesign: Window > Output > Separations Preview. Toggle each plate off in turn. The HP plate should carry the specialty artwork and nothing else, and the CMYK plates should show no hole where it sits. This is the most reliable check there is, because it is the same thing the RIP will see.
Check the PDF in Acrobat
Tools > Print Production > Output Preview, with Simulate Overprinting checked, shows the separations in the exported file rather than in the working document. It is the last thing to look at before the file leaves your desk.
Common Mistakes to Avoid
These are the ones we see most often, and every one of them looks fine on screen until Overprint Preview is on.
Fill on, stroke off
Outlined type with a stroke knocks out along its stroke while the fill overprints. Check both boxes whenever there is a stroke.
A CMYK object set to overprint
Usually inherited from a copied specialty element. The color shifts on press because both inks print. Overprint belongs on the specialty inks only.
The name is almost right
"HP White", "hp white 1" and "HP White 1" are not HP White 1. The separation is found by name, and a near miss prints as a gray CMYK build.
Trusting the screen
Knockout and overprint are indistinguishable with Overprint Preview off. Turn it on, or open Separations Preview, before you decide the file is done.
If you are not sure a file's overprint is right, send it over anyway. Checking a separation takes us a couple of minutes; a reprint takes a good deal longer, and we would much rather do the first.